Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of hospital- and community-acquired infections. MRSA has been identified as a serious threat to public health by the Centers for Disease Control and Prevention. Many antibiotics on the market are no longer effective in treating MRSA infections, which results in >11,000 deaths a year in the United States alone. The currently approved antibiotics for treating MRSA infections are vancomycin, linezolid, ceftaroline, and daptomycin, of which only linezolid can be dosed orally. In addition, resistance has been documented for all four of these approved drugs. This underscores the importance to develop new, orally available antibiotics that can effectively treat these bacterial infections. We have discovered a new class of antibacterial agents, the quinazolinones, which are effective in a mouse model of MRSA infection and characterized their mechanism of action. The lead quinazolinone is water soluble, has good oral bioavailability, low clearance, and is not toxic; however it has a modest volume of distribution. The quinazolinone binds to the allosteric site of penicillin-binding protein (PBP) 2a, an enzyme involved in cell-wall synthesis, and triggers opening of the active site. This proposal aims to perform lead optimization of the quinazolinone class, to investigate the synergy between the quinazolinones and other antibiotics, and to further investigate the mechanism of action of the quinazolinones. This proposal is an interdisciplinary project that involves organic synthesis, biochemistry, microbiology, structural biology, pharmacology, and animal models of infection. These studies will expand our knowledge in designing effective anti-MRSA compounds and understanding this new class of antibacterials.